POWRE: Analysis of Space-clamp Errors in Voltage-clamp Experiments on an Extended Neuron

本研究项目的目标是更好地了解在实验神经生理学和生物物理学中使用重要的测量程序(“电压钳”)时可能出现的严重类型的错误。电压钳方法被广泛用于定量表征神经元中离子通道的特性。当电压钳位施加到某些单元时，该过程中的固有缺陷会引起所谓的“空间钳位误差”。为了使电压钳准确地测量细胞膜上的离子电导，必须测量电压没有空间变化的膜片上的电流。然而，在许多研究应用中，没有一种实用的方法来实现位势的空间一致性。例如，在神经生理学中，附着在神经细胞体上的轴突和树突(即长的或“延伸的”神经元)是空间电压变化的常见来源。有时可以修改实验程序以减少空间钳位误差；然而，结果并不总是令人满意的，这种修改的范围是有限的。另一种选择是基于数学模型和计算机模拟的实验后分析和修正。本项目将进行这样的分析。具体地说：(1)将对扩展神经元简化模型的电压钳位引起的空间钳位误差进行计算机模拟；(2)将基于对最初为没有活性通道的膜开发的“电缆方程”的修改，建立具有活性离子通道的神经元的数学模型。然后，将对模拟结果和拟合的数学模型进行分析，以便评估空间夹误差的性质和大小，并制定识别和纠正这些误差的标准。这个POWRE项目将使Castelfranco博士在经历了几年的非自愿中断后，能够重返与她的训练和科学兴趣一致的数学神经生理学研究计划。此外，这将把她在母校的正式身份转变为一种可以增加她获得资源的机会，并提高她研究的知名度。

The goal of this research project is to better understand a serious type of error that can arise when an important measurement procedure (the "voltage clamp") is used in experimental neurophysiology and biophysics. Voltage-clamp methods are widely used to characterize quantitatively properties of ionic channels in neurons. An intrinsic defect in the procedure gives rise to what are termed "space-clamp errors" when the voltage clamp is applied to certain cells. In order for the voltage clamp to yield an accurate measurement of ionic conductance across a cell membrane, the current must be measured across a patch of membrane with no spatial variation in the voltage. However, in many research applications there is no practical way of achieving spatial uniformity of potential. In neurophysiology, for example, axons and dendrites attached to a nerve-cell body (i.e., long or "extended" neurons) are a common source of spatial voltage variation. It is sometimes possible to modify the experimental procedure in order to reduce space-clamp errors; however, the results are not always satisfactory, and the scope of such modification is limited. An alternative is post-experimental analysis and correction based on mathematical models and computer simulation. This project will carry out such an analysis. In particular: (1) computer simulations will be carried out for space-clamp errors arising from voltage clamp of a simplified model of an extended neuron; and (2) mathematical models of a neuron with active ionic channels will be developed based on modifications of the "cable equations," which were originally developed for membranes with no active channels. The results of the simulations, and the fitted mathematical models, will then be subjected to analysis in order that the nature and magnitude of space-clamp errors can be assessed, and that criteria for recognition of, and correction for, these errors can be developed.This POWRE project will enable Dr. Castelfranco to return to a research program in mathematical neurophysiology consistent with her training and scientific interests, following an involuntary hiatus of several years. Moreover, it will transform her official status within her home institution to one that will increase her access to resources and raise the visibility of her research.